correct the error

correct two errors e(sub)i and e(sub)j in the extended ISBN number 2-37-952835-1-6 with 10th check digit x sub 10 is congruent to the sumation from i=1 to 9 of i * x(sub)i (mod 11)[/tex] and 11 check digit x sub 11 is conruent to the summation from i=1 to 9 of i^2 * x(sub)i, if we knnow that e(sub)i=e(sub)j-1